Re:So Thermodynamics Nazis... (Score 4, Informative)

Water vapor would be a powerful greenhouse gas, if there weren't already so much of it there. Basically, our atmosphere has so much water vapor, that every frequency of IR that can be absorbed by it is already fully absorbed. So more water vapor won't make a difference. CO2 and CH4, on the other hand, are potent greenhouse gasses because not only do they absorb IR, but they're pretty scarce our atmosphere.